The long-range objective of this project is an understanding of the factors which contribute to the normal development and maintenance of myelin. Carbonic anhydrase is an enzyme with a well defined physiological function involving fluid and ion fluxes and its presence in myelin suggests a similar function there. As part of our overall interest in myelin chemistry and function, we propose to study the role of carbonic anhydrase in the physiological processes which give rise to normal adult compact myelin. Specifically procedures are being developed for the purification of myelin carbonic anhydrase by affinity chromatography; methods will be developed for measurement of enzyme levels by a 3H acetazolamide binding assay. The activity, levels and rates of synthesis of myelin deficient genetic strains of mice and in adrenalectomized rats. In other tissues, carbonic anhydrase is regulated by steroids and comparable effects may occur in brain and specifically in myelin. We will carry out an in-depth study to determine the effects of adrenal steroids on myelin carbonic anhydrase and on myelin composition and structure. The enzyme ctivity and levels will be studied in adrenalectomized rats with and without replacement therapy and the possible induction of the enzyme by adrenal steroids assessed using a double isotope technique. Surgical adrenalectomy will be supplemented by pharmacological adrenalectomy in which specific inhibitors of either glucocorticoids or mineralocoritcoids are used. The effects of carbonic anhydrase inhibitors on myelination will also be studied. These studies are pertinent to understanding the normal naturation of myelin and the pathophysiology of a variety of demyelinating diseases in which vacuolization or splitting of myelin occurs; they should thus contribute to the development of more rational methods of treatment of these diseases. Since certain carbonic anhydrase inhibitors are used for the treatmnt of seizures during the period of active myelination, the studies on these inhibitors have particular clinical relevance.